Background: While epidemiological studies have demonstrated an association between ambient particulate[unreadable] pollution and adverse health effect, uncertainties still exist concerning specific properties of particles that[unreadable] affect pathophysiological mechanisms. Often it has been very difficult to reproduce ambient conditions in a[unreadable] laboratory with sufficient doses to elicit effects. The development of ambient particulate concentrators has[unreadable] bridged this gap, effectively merging the ambient environment with the laboratory. Concentrated ambient[unreadable] particle experiments have linked real-world particulate matter to a host of health effects observed in human[unreadable] and animal exposure studies as well as in vitro.[unreadable] Specific Aims: The objective of this 5-year project core, under the leadership of Dr Contantinos Sioutas, is to[unreadable] support project investigators and Center members who will be investigating the effects of ambient particulate[unreadable] matter on human health, including allergic inflammation. This core will provide chemically-characterized,[unreadable] concentrated ambient fine and ultrafine particle suspensions collected in downtown Los Angeles. The[unreadable] proposed project expands upon the NIEHS and US EPA funded research concerning the adverse health[unreadable] effects of particulate matter that has taken place at USC and UCLA over the past five years.[unreadable] Methods: Concentrated ambient fine and ultrafine particles will be collected by means of new and improved[unreadable] portable concentrators developed over the past five years by the University of Southern California, at a[unreadable] typical urban background site in downtown Los Angeles. The majority of the concentrated flow will be[unreadable] collected in aqueous suspension, immediately frozen with dry ice and transferred to UCLA for toxicity[unreadable] analysis. This procedure minimizes any possible chemical reactions in the suspension, maintaining its realworld[unreadable] characteristics. Aerosol characterization will include mass and chemistry measurements, including[unreadable] trace elements, inorganic ions, elemental/organic carbon, and PAHs.[unreadable] Relevance: The use of aerosol concentrators in conjunction with various in vitro and in vivo toxicity assays[unreadable] over the past five years has significantly improved researchers' understanding of health effects due to[unreadable] particles. Now that certain health endpoints have become the focus of experiments, the mechanisms[unreadable] leading to these endpoints can be investigated. Past studies have employed concentrators at various[unreadable] locations and seasons while emphasizing a variety of endpoints. By controlling these variables and[unreadable] enlarging the sample set, exploration into specific biological mechanisms behind observed health effects of[unreadable] particulate matter can begin.